Feedstock Energy Reporting Compilation for the Paving and Other Related Industries

Abstract

Feedstock energy is the combustible energy content in a material. This article analyzes the consistency in nomenclature and reporting of feedstock energy with respect to life cycle assessments (LCA) within scientific reports, environmental product declarations (EPDs), product category rules (PCRs), LCA tools, standards, and other documents. The paving industry and other relevant industries were identified for comparative purposes and consistency. A detailed inventory was compiled for the United States, with representative documents from other countries. There is some consistency in definitions of feedstock energy and related terms, but little consistency in how they are reported and/or compiled in EPDs, PCRs, and LCAs. Feedstock energy is sometimes allocated to different life cycle processes; it may be considered a material or an energy resource; and there is uncertainty as to whether total energy includes feedstock energy. In addition, the possibility for double counting may exist. Future efforts at harmonization schemes, especially in EPD reporting, are recommended.

Introduction

Life cycle assessment (LCA) is a methodology for quantitatively estimating the potential impact that a product or process may have on the environment over its lifetime and is based on the ISO 14040¹ and ISO 14044² standards. LCA usually relies on tracking uses of resources and emissions of substances throughout a product's life cycle by tracing the processes involved in producing, using, and disposing of the product. ISO 14040 requires an LCA to be calculated from cradle to end‐of‐life. The use of this methodology has been gaining momentum in private and public spheres.^3,4

Similarly, Environmental Product Declarations (EPDs), which are based on ISO 14025,⁵ are reports that present the results of an LCA methodology on a product up to a certain gate (e.g., prior to use), along with other relevant information, in a condensed and digestible format. Rules for creating an EPD for each specific product category type are laid out by various third parties in Product Category Rules (PCRs). These rules tend to be focused on more microscale details than the general requirements for LCAs or EPDs. In addition, these rules are made for a specific industry sector and product category, hence the name.

ISO 14040¹ defines feedstock energy as the “heat of combustion of a raw material input that is not used as an energy source to a product system, expressed in terms of higher heating value or lower heating value.” Various other industry groups and academic papers describe feedstock energy in essentially the same way.^6–8 A number of authors have discussed the appropriateness of including feedstock energy in cumulative energy demand, with some questioning whether it should be included for all products regardless of system‐wide implications.^9–11 Note that in many documents, the equivalent of feedstock energy is referred to as “use of nonrenewable primary energy used as raw materials.” This reference provides an opportunity to segregate out these items, but it may also cause confusion as to which category—material or energy or both—to use for feedstock.¹² According to Simonen, “sound judgment is required by the LCA practitioner” when deciding whether to treat substances as energy or material resources. Simonen uses crude oil as an example: It could count as an energy resource if combusted, or a material if used as plastic (both quantified in MJ).¹²

LCAs often include situations in which it is difficult to categorize the impacts of various processes or components in product systems or life cycle stages because they overlap or could have impacts in multiple systems. For example, there is no standardized process for deciding how allocations should be made in two common situations—recycling/reuse and processes with coproducts.¹³ For recycling, some of the common methods include the 50/50 method, recycled content method, and end‐of‐life method¹⁴; for coproducts, allocation might be by energy, mass, volume, or economic value.² Feedstock materials complicate the allocation issues even further with their availability as either a material or energy resource, or a combination of both. This article focuses on different nomenclatures of feedstock energy and provides a synthesis of how they are applied in various studies and life cycle products. The focus is mainly on the United States, but also includes examples from other countries.

Materials and Methods

First, ISO 14040¹ and ISO 14044² were analyzed to determine how these standards define feedstock energy and LCA and describe LCA requirements. This process provided some insights into how feedstock energy is expected to be used and its allocation.

LCA, life cycle inventory, and other environmental assessments were examined. Relevant material industries, which may include feedstocks with energy content, were determined to be paving, construction, roofing, wood, flooring, and plastics. Reports from organizations such as the American Society for Testing and Materials (ASTM) and the Federal Highway Administration (FHWA), EPDs and PCRs from the Product Category Rule Guidance Development Initiative,¹⁵ and databases and tools including the U.S. Life Cycle Inventory (U.S. LCI),¹⁶ GaBi U.S. extension databases, GaBi,¹⁷ and other tools were investigated.

Distinct from official definitions of the energy terminology is the question of how that terminology is interpreted and applied in published studies. Stakeholder considerations can drive important methodological decisions in LCA.¹⁸ Therefore, it is reasonable to assume that there may be variability in how energy definitions are interpreted and applied by various industries. Consideration needs to be given to the practices of many industries to determine if there is consensus on how these definitions are applied in studies.

Results

Feedstock Energy and LCA in ISO

The definition of feedstock energy is provided in ISO 14040 (and repeated in ISO 14044) with a special note: “Care is necessary to ensure that the energy content of raw materials is not counted twice.”¹ Therefore, the standards imply that when using a raw material that has an energy content that could be used for energy, but is not used for energy in the product or process system, then the heat of combustion of that material can be reported as the feedstock energy for the input. The requirements for energy inputs and outputs are further set by ISO 14044 as: “shall include inputs and outputs relevant for the production and delivery of fuels, feedstock energy and process energy used within the system.”² Additionally, ISO 14044 cautions that the risk of misunderstanding can result in double counting, and advises that allocation should be avoided wherever possible, for example by expanding the product system.

ISO 14040¹ specifically states that there is no single method for conducting an LCA and that organizations using these standards can implement the LCA in a manner related to the application thereof. It is also important to understand that during implementation of an LCA, the product or process system has inputs and outputs, and both of these are to be modeled, included in the data collection, and reported. In fact, ISO 14040 specifies that “ideally, the product system should be modeled in such a manner that inputs and outputs at its boundary are elementary flow.” Furthermore, in ISO 14040, LCA is from extraction through the end‐of‐life, and ISO 14044 requires that “deletion of life cycle stages, processes, inputs or outputs is only permitted if it does not significantly change the overall conclusions of the study.” In fact, ISO 14040¹ states that the LCA technique can be applied to studies that are not LCA, such as cradle‐to‐gate or gate‐to‐gate studies. In other words, an LCA with the requirements as set forth in ISO 14044² is for studies that are from extraction through the end‐of‐life. This is where feedstock energy is mandated to be reported, though not necessarily for the separate stages at various gates. In addition, even though the definition of feedstock energy in ISO 14040 is based on energy, there is no mention in the standard of material or its use as an energy resource.

Feedstock Energy Definition and Equivalent Nomenclature

The U.S. Federal Highway Administration (FHWA) guidelines say that feedstock energy should be included in LCA practices, but not necessarily where or how to include it.¹⁹ As such, the University of California Pavement Research Center (UCPRC) Pavement LCA Guideline²⁰ emphasizes that in the life cycle inventory phase the “feedstock energy must clearly be distinguished from combusted energy,” and in the material production phase, feedstock energy derived from materials that are used as a fuel should be included. Many groups, even within this one industry, use the term feedstock energy to mean different things. There is a widely‐used standard, BS EN 15804²¹ in which the equivalent of feedstock energy is referred to as “use of nonrenewable primary energy used as raw materials.” Further, the Athena Institute has published a report in which feedstock energy is classified as an energy source (the gross combustion heat value) even when it is not being used as an energy source. ²²

There may also be variability in how the information is presented in environmental product declarations (EPDs). EPDs are typically developed based on product category rules (PCRs), which are developed by various industries so that the EPDs within an industry have a similar basis and are determined using a similar methodology. Based on information from the American Center for Life Cycle Assessment (ACLCA),¹⁵ a list of ISO 14025⁵ program operators and other programs for LCA‐based environmental claims were obtained from each program operator's website. However, there is currently no official harmonization of PCRs, and therefore of EPDs, across industries. As such, an EPD for one material used for a particular construction object might not be comparable to an EPD for another material used for the same purpose.

The International EPD^® System²³ represents an example from the construction industry. Even though the term feedstock energy is not used in the report, use of nonrenewable primary energy resources used as raw materials [MJ, net calorific value] is listed in the raw materials supply phase and is reported in the environmental performance table. Canadian Standards Association (CSA)²⁴ includes another example for the paving industry in which materials in a nonrenewable material category are based on mass. An example EPD from the wood industry²⁵ has also reported material resource consumption in the same manner as CSA in a cradle‐to‐gate impact assessment. It should be noted that tracking feedstock as material with units of energy (kJ) is a possible alternative and is very common in many LCAs and in the literature regarding abiotic resource depletion (fossil fuel).²⁶

An LCA‐based software package developed by various collaborators and partners, Athena Impact Estimator (IE) provides models for buildings and highways²⁷ that use the Tool for Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) methodology²⁸ for calculating global warming, acidification, human health, ozone depletion, photochemical smog creation, eutrophication, and fossil fuel consumption potentials. The tool measures nonrenewable energy consumption in MJ and classifies it as a subset of total primary energy consumption, which includes all fossil fuels as well as nuclear. According to the Athena IE Handbook “embodied primary energy includes all energy, direct and indirect, used to transform or transport raw materials into products and buildings, including inherent energy contained in raw or feedstock materials that are also used as common energy sources.”²⁷

As one of the most widely‐used LCA tools,²⁹ GaBi (GanzheitlicheBilanz) has extensive database options, including its own database and integration with external databases such as ecoinvent, U.S. LCI, and others.¹⁷ GaBi uses a set of six indicators to measure primary energy consumption: 1.) primary energy demand from renewable and nonrenewable resources (both gross and net calorific value), 2.) primary energy from nonrenewable resources (both gross and net calorific value), and 3.) primary energy from renewable resources (both gross and net calorific value).

Building for Environmental and Economic Sustainability (BEES), a tool for analyzing the environmental and economic impacts of building products, was developed by the National Institute of Standards and Technology (NIST).³⁰ It accounts for the environmental impacts from energy consumption and combustion and reports embodied energy results in two ways: 1.) by fuel and feedstock energy, and 2.) by fuel renewability. BEES defines feedstock energy as “the energy content of fuel resources extracted from the earth, while fuel energy is the amount of energy that is released when fuels are burned.” For instance, if fuel resources such as petroleum and natural gas are used as material inputs, the energy value remains in the feedstock category. In contrast, whenever the extracted fuel resources are transformed into fuels and combusted to obtain energy, they are classified in the fuel category. Since bio‐based products and plastics have embodied energy, BEES indicates that they may generate higher feedstock energy values. In addition to feedstock energy, this tool can calculate the total embodied energy within the categories of renewable and nonrenewable energy.

Also developed by NIST, Building Industry Reporting and Design for Sustainability (BIRDS) provides an environmental and economic analysis of new commercial buildings including operating energy, environmental performance of materials, construction, and use and life‐cycle costing;³¹ and models different building types for different locales. In the BIRDS handbook, primary energy consumption is defined as “fossil fuel depletion when fossil fuel resources are consumed at rates faster than nature renews them.” The primary energy consumption is used to calculate the resource depletion side of fossil fuel extraction, given in kWh. The tools GREET,³² Umberto,³³ OpenLCA,³⁴ EIO‐LCA,³⁵ PaLATE,³⁶ and FEC³⁷ do not consider feedstock energy in their models.

In a study of LCA related to asphalt pavement, Butt et al. focused on the construction, maintenance, and disposal of asphalt pavements because of their high environmental impacts in terms of energy use and greenhouse gas emissions (CO₂, N₂O, and CH₄) during the lifetime of this material.³⁸ Special emphasis was given to the calculation and allocation of the energy used for binder and additives. The study found that the feedstock energy is highly valuable in terms of the cost of the binder since it may have an alternative value as a fuel. Butt et al. also indicate that feedstock energy in a life cycle study could be considered to be “borrowed from nature.” They considered feedstock energy for generating energy and also as stored within the asphalt materials when it is not consumed. In a paper on construction materials, Ventura and Santero tried to clarify the way feedstock energy is reported in LCAs⁹ and offered several definitions of primary energy, secondary energy, and process energy, indicating a relationship scheme between those energy types. Regarding feedstock energy, they suggest that “when organics are used as materials, the energy associated with much of this input remains incorporated in the product.” The paper cautions that primary energy should not be included in the inventory table, but total primary energy should be calculated because it is considered as a resource depletion indicator. This implies that feedstock energy, which is not combusted, is a loss of available resource. The contrast between Butt et al. and Ventura and Santero shows how feedstock energy is interpreted in two very different lights, one positive, the other negative.^9,38 Until more guidance or consensus standards are developed to include the life cycle of the items in a material or product EPD, these items are not likely to be consistently used in a fair comparative manner for material selection.

An interesting aside to these investigations is that the term nonrenewable is used to describe both energy and a material. Some energy resources are considered as nonrenewable and might therefore be categorized as nonrenewable with respect to feedstock energy; however, it is conceivable that it could be considered renewable given conservation of the resource. However, as per the European Commission,³⁹ some biogenic resources, such as primary forests or peat, are also considered to be nonrenewable. This illustrates the confusion about the term nonrenewable absent better definitions, especially with respect to time frames and recyclability. For instance, in terms of the pavement sector, if there are other reporting requirements that deal with material flows and the use of the asphaltic binder is included in those flows, then this may again be double counting of the material. Some studies report the use of nonrenewable energy sources, which would amount to double counting if the asphalt is counted both as using a nonrenewable energy source and as feedstock energy.

As previously mentioned, there are several expressions related to feedstock energy and its allocation in the literature, including reports from institutions and organizations, EPDs, PCRs, LCA articles, and tools or databases. Summaries of those references are compiled in Tables 1 and 2. Table 1 summarizes the different representations collected for feedstock energy application; and Table 2 indicates different statements of feedstock energy application and system boundaries classified by specific industries.

Table 1.

How Feedstock Energy or Equivalent Nomenclature Are Included in the Various Resources

Lettering Scheme	How feedstock energy or equivalent nomenclature are included in the various resources given in Table 2
A	Feedstock energy to produce materials should be allocated as material resources (kg), and process energy should be allocated as energy resources (MJ).
B	Recycled and recovered materials should be considered as raw materials and if they have fuel content and are used as fuels, they must be allocated as alternative energy.
C	Special care should be taken to consider impacts on the environment, e.g., energy content of the product for energy recovery in the end‐of‐life.
D	The use of nonrenewable primary energy excluding nonrenewable primary energy resources used as raw materials, and nonrenewable primary energy resources used as raw materials are reported separately in MJ.
E	Nonrenewable energy flows used to produce materials is counted separately and reported as nonrenewable fossil energy in MJ (removed from the nonrenewable materials section) and contributes to total primary energy consumption.
F	Each kg of finished product has a calorific value (feedstock energy) which can be converted into useful energy as a raw material.
G	Nonrenewable primary energy demand is expressed as MJ and nonrenewable material resources are reported as kg.
H	Energy content of biomass used for feed or food purposes shall not be considered in the LCA report.
I	Feedstock energy in a life cycle study could be considered as “borrowed from the nature.”³⁸ It is considered for generating energy and as stored within the asphalt materials when it is not consumed.
J	In the life cycle inventory phase, the “feedstock energy must clearly be distinguished from combusted energy,”²⁰ and in material production phase, “feedstock energy of materials that are used as a fuel”²⁰ should be included.
K	Feedstock energy is defined as “when organics are used as materials, the energy associated with much of this input remains incorporated in the product.”⁹
L	Nonrenewable energy sources without energy content (kg) is reported in Use of Resources without Energy Content table⁷³ and nonrenewable resources with energy content (MJ‐thermic) is reported in Use of Resources with Energy Content table.⁷³
M	Feedstock energy is “the energy content of fuel resources extracted from the earth, while fuel energy is the amount of energy that is released when fuels are burned.”³⁰
N	Feedstock energy is “the gross combustion heat value of any fossil hydrocarbon material input to a product system which is an energy source but is not being used as an energy source including its related pre‐combustion energy.”²²
O	Feedstock is tracked as a material with units of energy (kJ) under abiotic resource depletion of fossil fuels.

Table 2.

Feedstock Energy or Equivalent Nomenclature in Studies, PCRs, EPDs, and Tools

Industry	Lettering Scheme	Type	System Boundary Considerations	References
Paving	A	PCR	cradle‐to‐gate	40
	B	PCR	cradle‐to‐gate	41, 42, 43, 44, 45, 46
	C	PCR	cradle‐to‐gate	42, 47, 48
	C	PCR	cradle‐to‐grave	49
	D	PCR	cradle‐to‐gate and construction stage	50
			cradle‐to‐gate, cradle‐to‐site, cradle‐to‐gate with options	51
			cradle‐to‐grave	51, 52
		EPD	cradle‐to‐gate	53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65
		EPD	cradle‐to‐gate with options	66, 67
	F	EPD	cradle‐to‐grave	68
	G	EPD	cradle‐to‐gate	69
	H	PCR	cradle‐to‐grave	49
	I	LCA	cradle‐to‐grave	38
	J	LCA	cradle‐to‐grave	70, 71, 72
	K	LCA		9
	L	EPD	cradle‐to‐gate	73
	N	Report	cradle‐to‐gate	22
Construction	C	PCR	cradle‐to‐grave	74
	D	PCR	cradle‐to‐gate, cradle‐to‐gate with options	75, 76
		PCR	cradle‐to‐grave	74, 76
		EPD	cradle‐to‐gate	77, 78, 79, 80, 81, 82, 83, 84, 85
			cradle‐to‐gate with options	23, 86
			cradle‐to‐grave	87, 88, 89
	M	Tool		30
Wood	B	PCR	cradle‐to‐gate	90
	D	EPD	cradle‐to‐gate with options	91, 92
	G	EPD	cradle‐to‐gate	25, 93
Roofing	A	PCR	cradle‐to‐gate	94
	E	PCR	cradle‐to‐gate, cradle‐to‐grave, cradle‐to‐gate and end‐of‐life	95
		EPD	cradle‐to‐gate	96, 97, 98, 99
		EPD	cradle‐to‐building with end‐of‐life stage	100
	G	EPD	cradle‐to‐gate and end‐of‐life	101
Flooring	C	PCR	cradle‐to‐gate	102
Flooring	O	PCR	cradle‐to‐install and end‐of‐life or cradle‐to‐grave	26
Plastics	H	PCR	cradle‐to‐gate, gate‐to‐gate, or gate‐to‐grave	103
Multiple Industries	G	Tool		17, 104

Discussion

This article evaluates the standard of practice for reporting feedstock energy in various documents such as industrial reports, EPDs, PCRs, LCA articles, tools and standardization documents, mainly in the United States but also in other countries. The following summarizes the findings from the reviews of the nomenclature used and how feedstock energy was allocated in that reporting.

Three similar types of nomenclature were compiled from the reviewed studies. They are for impacts: abiotic resource depletion (fossil fuels), and for use: nonrenewable primary energy used as raw materials and feedstock energy.

It was found that there were various schemes for allocation of feedstock energy, which can be considered in two different ways: 1.) to determine if feedstock energy should be allocated as a material or an energy resource, and 2.) to determine how to define feedstock energy—as a process, stage, or product within an LCA, or a combination.

Table 1 and Table 2 indicate that there are also numerous different types of reporting approaches, particularly for feedstock energy. First, the units differ in the schemes, with some as energy and some as mass. Second, even though some guidance is given on where to include or exclude feedstock energy, in some of the reviewed documents, many simply give a definition. Few provide details on methodologies for allocation throughout the full life cycle. In addition, the various sources have different system boundaries. As previously noted, an LCA in ISO 14040¹ should consider feedstock energy and is for a full cycle. However, there is no distinction on where or for what reason it should be considered in this standard, although the warning about double counting is included.

Therefore, the consideration of feedstock energy in the sources shown in Table 1 when the system boundary is to gate may be confusing. If feedstock energy is reported to gate, should it be listed in a manner that implies use of a resource or availability of a resource?—in other words, as a negative, positive, or neutral resource impact. Recall that Section 5.2.3 of ISO 14040 specifically states that “ideally, the product system should be modeled in such a manner that inputs and outputs at its boundary are elementary flow.”¹

Feedstock energy and related terminology are fairly recent additions to LCA standards, and until these practices are more fully developed or harmonized, the use of these terms in EPDs for material selection may not be comparative or useful. ISO 14040 requires that LCAs are from cradle to end‐of‐life.¹ However, most of the EPDs in the paving, construction, wood, and other industries are typically to a gate such as prior to use. Thus, these EPDs may not be capturing the possible benefits of feedstock energy for storage, recycling, energy use, and others. Future research looking to schemes for capturing this information in EPDs is recommended.

Footnotes

Acknowledgments

This project was supported by the National Asphalt Pavement Association (NAPA). The authors would specially like to thank Quinn Langfitt, Heather Dylla, Richard Willis, and Carter Ross for their ideas and help in development of this work.

Author Disclosure Statement

No conflicting financial interests exist.

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68.

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69.

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70.

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83.

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86.

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87.

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88.

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89.

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90.

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91.

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92.

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93.

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94.

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95.

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101.

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102.

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103.

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104.

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